The last two decades have witnessed a growing interest in the effect of metalinguistic awareness on learning foreign languages and in developing learners’ multilingual system (e.g., Jessner, 2006, 2014; Kemp, 2001; Nation & McLaughlin, 1986; Renou, 2001; Takahashi, 2005). Being a psycholinguistic concept and a subcomponent of metacognition, MLA is perceived as a fundamental element in multilingual development from a Dynamic Model of Multilingualism (DMM) perspective (Herdina and Jessner, 2002), maintaining that complex and dynamic interactions between multiple languages in the brain influence the development of the entire multilingual system (Jessner, 2008; Jessner, Allgäuer-Hackl & Hofer, 2016). MLA researchers have indicated that speakers who use their metalinguistic abilities to gain insights into the given target language based on crosslinguistic similarities and differences can easily decode new structures, including syntactic and semantic constraints of that particular language (Peyer, Kaiser, and Berthele, 2010; Singleton and Aronin, 2007). MLA is suggested to have a catalytic effect in learning languages (Jessner and Allgäuer-Hackl, 2020) and is identified as the key factor in multilingual learning (Jessner 2006, 2008). From a DMM perspective, multilingual acquisition processes are enhanced by strong synergetic effects developed in experienced multilingual learners who seem to accumulate metalinguistic and metacognitive knowledge as multilingual learners and users (Jessner, 2019). One can thus assume that bi-/multilingualism is associated with the development of metalinguistic ability and awareness. However, it has been suggested that a positive relationship between bi-/multilingualism and MLA depends on a certain number of social, psychological and educational factors (Titone, 1997). These factors can be referred to as ID variables perceived as multi-componential, integrated, dynamic and complex variables (Dörnyei, 2009) influencing, generally, the process of language learning, and particularly, metalinguistic awareness (Jackson, 2014). Motivation as a psychological construct affecting the process of second and foreign language learning and strongly linked to a learner’s success at learning languages (Bower, 2019; Csizer and Dörnyei, 2005; Dörnyei, 1998, 2001; Gardner, 1985) has been studied with relation to MLA and has been proven to affect learners’ metalinguistic ability (Takahashi, 2005; Titone, 1997). In a similar vein, proficiency is another ID variable that has been suggested to reflect metalinguistic awareness (Renou, 2001). However, in light of the growing body of MLA research, only few researchers have investigated the interaction of these individual difference variables, namely motivation and proficiency, with learners’ metalinguistic awareness (e.g., Amjadiparvar and Zarrin, 2019; Renou, 2001; Takahashi, 2005). Hence, a further investigation can be carried out to probe into the relationship of MLA with learners’ motivation and proficiency.